Chapter 25 - Electromagnetic Waves - Problems and Conceptual Exercises - Page 900: 16

$1.7\times 10^8m$

We know that $t=\frac{2d}{c}$ We plug in the known values to obtain: $(1-0.15c)=\frac{2d}{\frac{2d}{c}+\Delta t}$ $\implies 0.85c=\frac{2dc}{2d+c\Delta t}$ $2d+c\Delta t=\frac{2d}{0.85}$ This simplifies to: $d=\frac{c\Delta t}{2(0.17647)}$ $d=\frac{(3.0\times 10^8m/s)(0.20s)}{2(0.17647)}$ $d=1.7\times 10^8m$